The present disclosure relates generally to electroluminescence (EL) display devices, and more particularly to the design of the metal lines used within the display devices.
Typical organic electroluminescence (EL) display devices comprise a plurality of organic light emitting diode (OLED) elements (pixels) which are connected and arranged in a matrix array construction. Each OLED pixel is equipped with a switching and a driving circuit, usually comprised of capacitors and thin film transistors (TFTs) connected to scan, data and power lines. The combination of these circuits and lines serve to provide display information and power for each OLED pixel. Image display information is sent to the matrix of OLED pixels via routings of the scan, data and power lines that are connected to each OLED pixel-circuit set.
The three line types, scan, data and power, are comprised of conducting metal alloys. Conducting metal alloys featuring low resistivity material property are used as the lines to help maintain low operating resistance minimizing the voltage drop effects due to the material properties of the lines. Resistance may be defined by the following resistance equation for a solid rod or line material:R=□*L/A wherein □□ is the resistivity constant for the given material, L is the length of the rod or line material, and A is the cross-sectional area of the rod or line material. The relationship of resistance to voltage is described by Ohm's Law:V=R*I, wherein the voltage (V) drop across a given material for a passing current (I) is dependant upon the electrical resistance (R) of the conducting material. The construction of the display device's matrix array requires metal line routings of different lengths to each OLED pixel-circuit set from the originating scan, data, and or power sources. The varying routing lengths of the metal lines effectively impose varying in-line resistance values onto the various OLED pixel-circuit sets. As a result, the delivered voltage level to the OLED pixels and their associated circuits may not be the same for all OLED pixel locations of the EL display device's matrix array.
Advanced EL display devices feature high performance image display qualities such as brightness, contrast, resolution, colors, flicker, distortion and linearity. In addition, advanced EL display devices may feature high operational refresh speeds, as well as low overall power consumption. Varying and unbalanced levels of voltage between the OLED pixel locations of such advanced EL display devices may counteract and cause undesired effects upon the image display qualities, as well as to the operational speeds and power consumption. While efforts have been made to utilize metal lines featuring low resistivity (□) material, more focus is needed upon the other contributing factors (e.g.; length L and cross-sectional area A) to lower the resistance (R) of the metal lines.
What is desirable is an improved method for the fabrication of metal lines that features lower resistance throughout the different routings and lengths to the pixel locations.